1. Field of the Invention
The present invention relates to a zoom lens system suitable for video cameras, electronic still cameras and the like using a solid state imaging device.
2. Description of Related Art
As increasing trend of video cameras and electronic still cameras to be compact, a request for zoom lens systems to be compact has become strong. Recently, a request for a zoom lens system having a function of varying zoom ratio has increasingly been strong. Moreover, as an increasing request for high imaging quality, the number of pixels of an imaging device has become large resulting in a strong request for high optical performance. As a means for accomplishing these requests, a zoom lens system using a diffractive optical element has been known.
For example, a zoom lens system consisting of, in order from an object, negative-positive, two lens groups, having a diffractive optical surface on at least one lens surface of a first lens group or a second lens group was disclosed in Japanese Patent Application Laid-Open No. 11-52235. Moreover, a zoom lens system consisting of, negative-positive-positive, three lens groups having a diffractive optical surface in any one of the three groups was disclosed in Japanese Patent Application Laid-Open No. 11-52237. Furthermore, a zoom lens system consisting of, negative-positive-positive, three lens groups having a diffractive optical surface in the second lens group was disclosed in Japanese Patent Application Laid-Open No. 2000-221397.
However, in any one of zoom lens systems disclosed in Japanese Patent Application Laid-Open Nos. 11-52235 and 11-52237, both optical performance and compactness were not sufficient. In a zoom lens system disclosed in Japanese Patent Application Laid-Open No. 2000-221397, since a diffractive optical surface arranged in the second lens group was introduced at a cemented surface, it was difficult to manufacture.